Wiktionary
one big happy family
n. A group of people who get along well together.
Wikipedia
One Big Happy Family
One Big Happy Family is an American reality television series featuring the Coles family, an African-American family of four who reside in Indian Trail, North Carolina. The series premiered on TLC on December 29, 2009. The show deals with their family life and with their efforts to lose weight, (each family member, at the initial episode, weighed in excess of 330 pounds).
Usage examples of "one big happy family".
I mean, it's like the three of us sitting back there, in that drugstore place, like we're one big happy family or something.
She hadnt asked them to supper just for the joy of seeing them all seated around the table as one big happy family.